Method and apparatus for grinding gears



Nov. 3,1959 E. WILDHABER 2,910,808

METHOD AND APPARATUS FOR GRINDING GEARS Filed Jan. 15, 1954 I sShecs-Sheet 1 FIG. 7

0 INVENTV M E.W|LDHAB At't'orney 7F Nov. 3, 1959 E. WILDHABER METHOD ANDAPPARATUS- FOR GRINDING GEARS 3 Sheets-Sheet 2 Filed Jan. 15, 1954INVENTOR. E WILDHABER BY Nov. 3, 1959 E. WlLDHABER 2,910,808

METHOD AND APPARATUS FOR GRINDING GEARS Filed Jan. 15, 1954 3Sheets-Sheet 3 4 E WILDHABER LE /W BY A Him-nay United States PatentMETHOD AND APPARATUS FOR GRINDING GEARS Ernest Wiltlhaber, Brighton,N.Y.

Application January 15, 1954, Serial No. 404,224

28 Claims; (Cl. 51-55) The present invention relates to the productionof gears, and more particularly to the grinding of the tooth sides ofcylindrical gears, such as spur, helical and herringbone gears, worms,etc. In a more specific aspect, the invention is especially useful inthe grinding of the tooth sides of helical gears and worms.

A primary object of the present invention is to provide a method andapparatus for grinding the tooth sides of cylindrical gears'withsubstantially flat or plane-faced grinding wheels so that the same wheelor wheels can be used in grinding gears of a given normal pitchregardless of their tooth numbers.

Another object of the invention is to grind the tooth sides ofcylindrical gears with flat or plane-faced grinding wheels in such a wayas to produce localization of hearing or ease-off at the tooth ends.

Another object of the invention is to grind the tooth sides ofcyindrical gears with localization of hearing or ease-off at the toothends, where the ease-off is under full control as to where it isapplied.

Another object of the invention is to grind the sides of helical teethwith fiat-faced grinding wheels in such a way that the teeth of matinggears bear in a localized area when run in their exact meshing positionunder light load, and that the shape of this tooth bearing area can becontrolled and altered at will.

Another object of the invention is to provide a method of and means forgrinding involute helical gear teeth with a pair of flat-faced grindingwheels in a helical grinding motion, but without the use of generatingroll and in such way that the grinding contact on opposite sides of theteeth ceases nearly simultaneously at the tooth ends.

Still another object of the invention is to provide a method andapparatus for grinding helical teeth with eased-off tooth ends with apair of flat-faced grinding wheels in unidirectional grinding passes,where the wheels are moved depthwise into and out of engagement with theworkpiece at the two ends, respectively, of the grinding strokes, sothat the wheels will be clear of the workpiece during each return strokeand so that the work may be rotated during each return stroke to permitthe grinding wheels to enter different tooth spaces on successivegrinding strokes.

A further object of the invention is to effect ease-off or localizationof tooth bearing in helical gears by advancing the grinding wheelstoward the surfaces engaged thereby adjacent both ends of the grindingstrokes, and by turning the wheels very slightly about parallel pivotsin time with the grinding strokes, and about the same pivots about whichthe wheels are adjusted to conform with the helix angle of the teeth.

A still further object of the invention is to provide a method andapparatus for grinding helical gears with two wheels, in which thegrinding wheels are advanced work, and along a line inclined at an acuteangle to the axis of each wheel.

Still another object of the invention is to provide a method forgrinding gears of the character described which can be performed on arelatively simple machine.

Other objects of the invention will be apparent hereinafter from thespecification and from the recital of the appended claims.

In the drawings:

Fig. 1 is a view illustrating one embodiment of the present inventionand showing a flat faced. grinding wheel in grinding engagement with ahelical gear;

Fig. 2 is a fragmentary section taken at right angles to the axis of thegear of Fig. l, and showing the gear in full but showing the grindingwheel only fragmentarily;

Fig. 3 is a view of a tooth of the gear showing the line of contactbetween the tooth surface and the substantially fiat grinding surface ofthe wheel;

Fig. 4 is a view illustrating another embodiment of the invention,showing a grinding wheel in grinding engagement with a helical gear butshowing the grinding wheel partly in section;

Fig. 5 is a section similar to Fig. 2 taken at right angles to the gearof Fig. 4 and showing the grinding wheel only fragmentarily;

Fig. 6 is a View, similar to Fig. 3, of a gear tooth, taken along theaxis of the grinding wheel of Figs. 4 and 5 and showing the line ofgrinding contact between the wheel and tooth;

Fig. 7 is a view, similar to Fig. 3, of a gear tooth, showing the effectof lengthwise ease-off or localization of the tooth bearing;

Fig. 8 is a view, similar to Fig. 7, of a gear tooth showing the desiredform of complete ease-off, consisting of lengthwise and profilewiseease-off or localization of the tooth bearing;

Fig. 9 is a diagrammatic view, corresponding specifically to Figs. 4 to6, and showing how lengthwise ease-off at the tooth ends is attained bythe present .invention;

Fig. 10 is a somewhat diagrammatic view, similar to Fig. 4-, but showingthe use of a pair of grinding wheels for simultaneously grindingopposite sides of the teeth of a helical gear, and showing also wheelswith slightly internal grinding surfaces;

Fig. 11 is a section through the gear of Fig. 10 taken at right anglesto the gear axis and showing fragmentarily only the grindingwheels whichare in engagement therewith;

ing a pair of grinding wheels having substantially plane grindingsurfaces in engagement with a gear blank, the contour of the gear blankbeing indicated in dotted lines; Fig. 13 is a diagram corresponding toFig. 12 and illustrating the way of obtaining controlled easeoff orlocalization of tooth bearing;

Fig. 14 is a more or less diagrammatic view illustrating theconstruction of a grinding machine for practicing individually forease-off in the same direction, in which they are moved depthwise intoengagement with the the present invention and showing particularly thead justments and motions required;

Figs 15 is a diagrammatic view, similar to Fig. 14, and showing amachine constructed according to another embodiment of the invention;

Fig. 16 is a view, partly broken away, taken at right angles to the viewof Fig. 15 and in a direction perpendicular to the axes of the grindingwheels; and

Fig. 17 is a fragmentary axial section of the control cam andcooperating parts of the machine of Figs. 15 and 16, the section beingtaken in a plane perpendicular to the drawing plane of Fig. 16.

In the method of the present inventionflat or plane surfaced grindingwheels are employed; and the tooth pro- Fig. 12 is a diagrammatic view,similar to Fig. 4, showfiles produced are preferably of involute form.The profile of the grinding surface in an axial section is substantiallystraight and does not change with change in wheel diameter. The samewheel profile is used during the whole life of the wheel. Preferably twowheels are used, for grinding, respectively, opposite sides of theteeth. The two Wheels are set so that their grinding surfaces face eachother. Ease-01f is attained by advancing the wheels toward the toothsurfaces engaged thereby at the ends of the grinding strokes. The wheelsare turned very slightly about parallel pivots in time with the grindingstrokes, and about the same pivot about which the wheels are adjusted toconform to and produce the helix angle of the teeth. The grinding wheelsare advanced individually for ease-off in the same direction in whichthey are moved depthwise into engagement with the Work piece, that is,each is advanced along a line inclined at an acute angle to the axis ofthe grinding wheel.

Referring now to the drawings by numerals of reference and first to theembodiment of the invention shown in Figs. 1 to 3 inclusive, 20 denotesthe grinding wheel, and 21 the gear which is to be ground, here ahelical gear. The grinding Wheel may have a plane or flat grindingsurface 22 which is perpendicular to the axis 23 of the wheel. The flatsurface 22 of the wheel will then contact a side 25 (Fig. 3) of a tooth26 of the work along a line 27 which passes through a mean point 28 ofthe tooth profile.

One aim of the present invention, however, is to achieve localization oftooth bearing, or ease-01f of the mating tooth surfaces at the toothends.

Profile ease-off is attained according to one embodiment of theinvention by slightly curving the profile of the grinding surface. Thisis indicated with much exaggeration in Fig. 2 at 30. The tangent 29 atmean point 28 to the grinding profile 30 of the wheel lies in a planeperpendicular to the wheel axis. If the profile were exactly straightand coinciding with the tangent 29 then the grinding surface would beexactly a plane. The grinding profile 30 used is very slightly concaveand contacts the tangent 29 at mean point 28. It departs from thetangent 29 at the ends of the active grinding surface in accordance withthe small amount of profile ease-otf desired on the gear teeth. It wouldnot be visible in the drawing unless exaggerated. It does not show upvisibly in the shape of the line of contact 27 (Fig. 3). Withoutease-off the grinding line 27 is exactly a straight line, which can beconsidered the proiection of a line parallel to the axis of theworkpiece. This line may pass through any point of contact. as point 28.

Fig. 3 shows that the whole working depth of the tooth surface 25 may becovered by grinding lines 27. provided that the grinding wheel issufficiently large. 7 The outline of the grinding wheel is shown indotted lines at 20'. Point 31 is the point at which the line 27 comesclosest to the axis of the grinding wheel. It is the projection of thisaxis to the grinding line 27. This point should be well'ontside of thetooth side 25 to avoid or reduce uneven Wheel wear. Each element of theline 27 has a counterpart on the axial profile of the grinding surface,acorresponding element of the axial profile. The latter element issmaller than the element of line 27, and has a varying proportionthereto. At point 31 this proportion is zero. This means that the wheelprofile tends to wear otf rapidly at this point.

With a large enough wheel the point 31 can be kept well outside of theactive portion of the grinding line 27. The wheel should also be largeenough and be so positioned that the grinding line 27 reaches far enoughdown on the tooth profile so that the entire working surface of theteeth is swept thereby.

The grinding Wheel is set to the helix angle of the teeth 26, at themean point 28, by adjusting it about a radial pivot 65 passing throughpoint 28; and it is inclined at the pressure angle of the tooth atthatpoint. The grinding plane, or its tangent plane at 28, is then inclinedto said pivot at the normal pressure angle at 28.

It truly helical teeth are desired, without ease-off at the tooth ends,then the grinding process would consist solely in providing a feedingmotion between the rotating wheel and the workpiece 21 along and aboutthe axis 35 of the workpiece, whereby the motions along and about theaxis 35 are in constant proportion. No additional generating roll isrequired where large wheels are employed.

Ease ofi at the tooth ends It has been tried to apply ease-off at theends of helical gear teeth by advancing the grinding wheel more towardthe tooth surface at both ends of the teeth. This advance depends on thefeed position, that is, on the distance of a considered position fromthe middle position, and is approximately proportionate to the square ofthis distance. It may be applied either'depthwise or normal to the toothsurface, for instance, along the wheel axis. But regardless of thedirection in which it is applied, it produces about the same result ifused alone. It can be demonstrated mathematically that the localizedbearing area thus obtained is bounded by inclined lines 56, whichcoincide with ditferent positions of the lines of contact between thetooth surface and the grinding wheel. It is the area between the dottedlines 56 in Fig. 7. This area extends across the tooth surface at abias. Here too much stock has been removed from the diagonal corners 57,and too little, if any, from the diagonal corners 58.

One object of the invention is to apply ease-01f exactly where it isdesired. Distinction should be made between lengthwise ease-ofi andprofilewise ease-off.

The lengthwise ease-off desired consists in easing oil the tooth endsstraight, without bias bearing. If we disregard profile ease-01f for themoment this means that when the mating gears are run on their exactcenters with a light load, they should bear in a localized area boundedat its ends by lines extending straight up and down the tooth profileslike the area between the straight lines 55 in Fig. 7.

The present invention permits attaining a substantially square orrectangular bearing area bounded by lines 55,

3 if profile ease-off is disregarded. It permits attaining an ovalbearing area 60 (Fig. 8) when profile ease-off is added to thelengthwise ease-off. This oval area produced by combined lengthwise andprofilewise ease-01f is the bearing shape generally desired. However,any other shape is also attainable in accordance with the presentinvention. Full control of the localization and ease-0E of the toothbearing is attained.

To secure truly helical teeth without lengthwise ease-off in theembodiment of Figs. 1 to 3 inclusive a rotating grinding wheel is fedalong the axis 35 of the workpiece and the workpiece is turned on itsaxis in time with said axial feed motion. The mean point 28 of grindingcontact thereby moves for instance from a position 28' (Fig. l) at thelower gear end to a position 28" at the upper gear end. The totalgrinding stroke is somewhat longer.

When ease-01f is applied at the tooth ends, the mean points of theeased-off end profiles should be ground in the immediate proximity ofthe points 28', 28" to avoid changes of pressure angle at those points.In other words, the flat faced grinding wheel 20 should not only beadvanced toward the surface being'ground, adjacent both ends of thegrinding passes, but it should also be tilted so that grinding-contactwill remain in the immediate proximity of the original contact positionat which ease-off is zero.

In accordance with the present invention the grinding wheel is tilted asit goes through the grinding path about the same axis aboutwhich it isset for the helix angle of the teeth or about an axis parallel thereto.Thus, it may be tilted about a radial axis 65 (Fig. 2) which lies in thedrawing plane of Fig. 2 and which projects as the point 28inFig.1.,

,This changing tilt corresponds to the changing helix angle of theeased-off tooth curve which passes through mean point 28 and is tangentto the helix at that point. The length of this curve increases with theface width F of the gear, and also depends on the helix 1,1.

cos t// In a development to a plane, the considered mean helix is astraight line; and the line which we want to substitute thereforethrough ease-oh? is a convex curve tangent to the straight line at itsmid point 28. The curve recedes from its mean tangent toward both endsto a given separation z at both ends. It increases essentially like thesquare of the distance from the mean point. Thus, at a distance halfwayfrom the middle to an end of a tooth it is onefourth of the separationat the end, that is, A z.

The inclination of the curve, or its helix angle, changes in directproportion to its length. On the side engaged by the grinding wheel inFig. 1, the helix angle changes from a larger value at or immediatelyadjacent point23 to its mean value at point 28, and to a smaller valueat point 28". The helix angle change is like the helix angle change of alarge circular are which has a given separation z at its ends from itsmean tangent.

The large radius R of this circle is tied up with the separation 2 atdistance It amounts to:

from its point of tangency 28 as follows:

The inclination i of the ends of the curve relative to the middle is theproportion of the distance 2 cos 1/ to the radius R F :4 cos ,b R inradian measure.

Through transformation This is the change in the helix angle from themiddle to one end point. The total change in helix angle from point 28to point 28 amounts to (2i Accordingly the grinding wheel should betilted or swung on pivot axis 65- in direct proportion to the feed alongthe gear axis 35 at a rate of (2i) between grinding positions 28 and2S". Simultaneously the grinding wheel should be advanced from theposition at zero ease-off toward the surface engaged thereby adjacentboth ends of the grinding strokes, to produce the required separationsof the eased-ofi curve from the truehelix.

This advance may be made in any desired direction. Of these directionstwo are especially attractive. One is along the axis of the grindingwheel, and the other along a straight line inclined to the wheel axis atan acute angle as will further be described.

This advance can be expressed mathematically in terms of the distance yof the grinding wheel position axially of the workpiece from its meanposition shown in Fig. 1. When the mean grinding point is in position28", then the corresponding distance y is equal to distance 28418" andequal to /2 F. The advance 2' is measured in terms of the separation itproduces. The actual movement of the grinding wheel is proportional to zbut may be difierent depending on the direction of advance.

Likewise the tilt i' of the grinding wheel at positions y can beexpressed as:

and i= ,9 2

Similar conditions exist in the embodiment of Figs. 4 to 6. Here too theadvance should be proportional to z and the tilt i should vary along thegrinding pass as expressed in Equation 2. In this case there is only oneangular setting between the grinding wheel and the workpiece. It is thesetting for helix angle. The grinding plane, that is, the tangent planeto the grinding surface at mean point 28, is inclined to the gear axis35 at an angle known as the base helix angle in the case of involuteteeth. It can be considered as obtained from the helix angle andpressure angle inclination of the axis 23 of the grinding wheel 20 (Fig.l) by turning this axis about the gear axis 35 until it is parallel tothe drawing plane. Its angular position then coincides with the angularsetting of the axis 43 of the grinding wheel 40 shown in Fig. 4.

As shown in Fig. 4, the grinding wheel 40 is bodily displaced ascompared with mean point 28. Its axis and body has a different positionlengthwise of the gear axis 35 than the mean point 28 around whichgrinding con tact centers. It is displaced toward the upper end of thegear 21, that is, it is displaced from the point 28 toward the side ofincreasing distance of the grinding surface from the axis 35 of thegear. The reason for this is readily seen in Fig. 6. It is bodilydisplaced so that its outline 40' more closely follows the tooth bottomand embraces the grinding line 27 to a sufficient depth. In this Way thegrinding line within the wheel outline covers all of the working depthof the tooth. Profile ease-cit may be attained, as in. the embodiment ofFigs. 1 to 3, by using a wheel profile 50 which is very slightly concaveand which contacts the tangent 49 at mean point 28 of the workingprofile. As before, this tangent lies in a plane perpendicular to thewheel axis. As before, the wheel profile would not show up dilterentfrom its tangent if its curvature Were not greatly exaggerated in Fig.5.

The relationship between z and i expressed in Equation 2 produces asquare bearing essentially as indicated in Fig. 7 by the full lines 55,or it can produce a hearing such as indicated at in Fig. 8 when profileease-off is added.

Any changes can be madein the shape of the tooth bearing area ifdesired. To slant the bearing toward the direction of the dotted lines56, an angle i is used which is smaller than given by Equation 2. Toslant the tooth bearing in the opposite direction an angle 1' is usedwhich is larger than given by Equation 2. The amount of easeoff can bechanged by assuming a difierent separation 2.

Fig. 9 illustrates the ease-off procedure diagrammatically as applied tothe embodiment of Figs. 4 to 6. The heavy lines indicate the grindingplane. The middle position corresponds to Fig. 4 with grinding contactat mean point 28. In the initial position 741), where grinding contactis made immediately adjacent position 28' of the mean point of theunrelieved profile, the grinding plane is tilted at the aforesaid angle1' to its mean position 70. At the end position the grinding plane 70"is tilted at the same angle i to its mean position, but it is tilted inthe opposite direction. During the grinding pass from 28 to 28" thegrinding plane is swung continuously in one direction in proportion tothe feed lengthwise of the gear axis 35. It is swung about a pivot axisperpendicular to the drawing plane of Fig. 9 and coinciding with thevarious positions of the mean point of grinding contact. During thegrinding pass this axis passes through positions 28', 28, 28".

Adjacent both ends of the grinding pass the wheel is its position atzero ease-off. Its advance corresponds to 2' as given in Equation 1, andto z in the positions 28, 28". The grinding planes 70' and 70" are. seento be advanced over the positions 28', 28" which correspond to zeroease-off. The advance, as well as the angle i, are very much exaggeratedin Fig. 9.

In practice it is desirable to swing the grinding plane about an axisofifset from the mean grinding point, as, for instance, about an axiswhich is at 72 in the mean grinding position and at 72', and 72" at thepositions corresponding to position 28', 28", respectively. The advanceof the grinding wheel with respect to its new pivot then has to bealtered accordingly. In view of the very small motions involved themathematical procedures applying to infinitesimal displacements can beused with high accuracy. The distance of the grinding plane 70" from newpivot 72" is made up of the distance of the grinding plane from pivot28" and of the distance of pivot 72 from the grinding plane if thisplane were to pass through point 28".

If the inclination of the grinding plane 70 to the direction of the gearaxis 35 is denoted by mp and x denotes the distance 2872, which is equalto 28'-72 and to 28"72, then the advance z" of the grinding wheel alongits axis, as compared with its middle position is found to amount to:

at any position y. The rate of advance is no longer zero at the middleposition. But it still is an advance at a varying rate at least on oneside. It may be a negative advance or withdrawal on the opposite side.

When the new pivot is displaced in the opposite direction as, forinstance, to 75 in the middle position, and to 75', 75" in the endpositions, then the distance x =2875 should be introduced as a negativequantity in the above equation for z".

The above equation applies for lateral displacements of the pivot in aplane perpendicular to the gear axis. If the pivot is displaced adistance x in normal direction, that is, perpendicular to the grindingplane 70, then the advance of the grinding wheel from the new pivotamounts to:

The second term is negligible. In this case then the advance z ispractically unchanged by the normal pivot shift. Any general pivot shiftcan be made up of a lateral shift x and a normal x Two grinding wheelsWhen two wheels are used, both wheels are preferably mounted on axeswhich are parallel in the middle position of the grinding stroke, withtheir substantially flat grinding surfaces facing each other.

7 Figs. 10 and 11 illustrate one such case. In Fig. 10 the gear 21 isindicated by its contour and by its axis 35 only. The axes 82 and $3 ofthe two grinding wheels 80 and 81 are here parallel; and the twogrinding wheels are seen to be bodily displaced relative to each otherlengthwise of the gear axis 35. In other words, they have differentaxial positions. These are provided for the same reasons as describedfor a single wheel with reference to Figs. 4 to 6. They enable thewheels to let the grinding line go down far enough toward the toothbottom.

Figs. 10 and 11 also illustrate a feature of a modification of myinvention. Here the profile ease-off is not attained by using a slightlyconcave grinding profile on an otherwise plane wheel surface. It isattained with a straight grinding profile 84 on a grinding surface 85 or86 which is slightly internal.

The grinding surface ishere an internal conical surface which contactsthetooth surface in a very slightly concave curve. In the-mid positionshown in Figs. 10

and 11 this line of contact passes through the mean point of contact 28for one wheel, and 28 for the other wheel. The tangent to said curve ateach of the points 28 28 lies in the theoretical, unrelieved toothsurface. At both sides of this point the curve reaches somewhat to theinside of the unrelieved surface, increasingly so with increasingdistance from said point. It thereby produces ease-off at the profileends.

Either way of producing profile ease-off on helical teeth may be usedwith a substantially flat grinding surface, or even a combination ofboth methods. The use of slightly internal grinding surfaces increasesthe distance between the two grinding wheels 80 and 81. When acombination of both described methods of achieving profile ease-off isused, it is done with the purpose of keeping the points of contact 28 atthe section perpendicular to the gear axis exactly mean points of thetooth profiles so that the two grinding lines have the same positionlengthwise of the gear axis.

When two wheels are used, the two engaged tooth profiles aresymmetrically positioned with respect to the center line of either atooth or atooth space. With this restriction the two described methodsof applying profile ease-off may give the desired position of the points28 only approximately if used one or the other. The combination of thetwo methods however permits overcoming this restriction and placing thepoint 28 at the exact height on the profile where it is desired. Itshould be understood, however, that satisfactory gears can be producedalso without placing point 28 at the exact middle of the height of thetooth profile.

Fig. 12 shows the use of a pair of wheels and 91 with essentially planegrinding surfaces 92 and 93. The wheel profiles of axial sections areconcaved so slightly that the curvatures does not show up in thedrawing. The wheel shape is like that described in connection with Figs.4 and S. The tangent at the mean point of the active wheel profile liesin a plane perpendicular to the wheel axis. As in Fig. 10 the flatgrinding surfaces 92, 93 face each other and the axes 94, 95 of thegrinding wheels are parallel in the mid position. The two wheels arebodily displaced with respect to each other along the axis 35 of theWork piece 21. Each wheel is advanced along the gear axis from thegrinding region toward the side of increasing distance from the axis 35of the workpiece.

Fig. 12 shows the grinding wheels more nearly in the right proportions.The grinding wheels employed in the present invention are preferablycomparatively large.

While Fig. 12 illustrates the mean position of the grinding pass orgrinding stroke, which is the same as for a helical gear withoutease-off, Fig. 13 diagrammatically illustrates with exaggeration thegrinding wheel positions when the mean points adjacent points 28', 28"of the end profiles are being ground. Both wheels are diagrammaticallyindicated by their essentially plane grinding surfaces. These havepositions 90, 90 and 91, 91" when the grinding region is at oppositeends of the gear teeth. In the positions 90', 91' as well as in thepositions 90", 91" the two wheels are tilted in opposite directions fromtheir mean positions; and their grinding planes are advanced beyond themean points 28 28 28 28 of the teeth without ease-off.

The positions of the wheel 91 have already been described fully withreference to Fig. 9. Diagonally opposite positions of the two wheelscorrespond to each other. Thus the wheel 90" at the left is inclined tothe axis 35 of workpiece 21 at the same angle as the wheel 91' at theright. It is advanced beyond the point 28 by the same amount as thewheel 91' is advanced beyond the point 28 The two wheels move together.Feeding motion between the pair of wheels and the workpiece is effectedalong the axis 35 of the work piece and about said axis in known manner.The motions along the axis 35 and about this axis are timed with eachother to produce the helical teeth. Ease-off at the tooth ends isobtained by advancing the wheels toward the tooth sides engaged therebyadjacent both ends of the grinding passes, and by swinging the wheelsslightly in opposite directions about axes passing through the meanpoints 28 28 of grinding contact.

The wheels may also be swung instead about other suitable axesperpendicular to the direction of the gear axis 35, for instance, aboutaxes 9-6, 97 at one end of the grinding pass, and about axes 96", 97"near the other end of the grinding stroke. When the grinding wheels areswung about displaced pivot axes, the advance of the wheels from thesepivot axes should be modified in the manner described with reference toFig. 9.

Grinding apparatus Fig. 14 is a diagrammatic view of one form of wheelhead constructed according to the present invention. in this view manyknown features have been omitted which do not pertain to the invention.What is shown is the novel arrangement of parts, and their displacementsor motion. 1

The grinding wheels 90 and 91 are rotatably mounted in holders 100, 101,respectively, and are driven by pulleys 102, 103 from a suitable powersource. The holders 100, 101 are swingable along ways 104, 105,respectively, about pivot axes 106, 107, respectively. The ways 104, 105form parts of slides 108, 109, respectively, which are adjustable alongways 110, 111, respectively, radially toward and away from the workpiece21. The ways 110, 111 are parts of a common slide 112, which isadjustable or movable along the axis 35 of the workpiece 21.

It should be noted that the pivot axes 106, 107 are offset from the axis35 of the workpiece. They are parallel; and they are perpendicular tothe direction of the work axis They are positioned on one side of therespective grinding wheels 90, 91, each on the side opposite to thegrinding side of the wheel. They intersect the axes 94, 9-5 of thewheels.

With the pivot axis offset in the manner shown the angular setting forthe helix angle displaces the grinding wheels bodily in the directiondesired so that the two wheels have different positions along the gearaxis 35. The radial adjustments of the slides 108 and 109 producedifferent spreads of the grinding faces as required on gears ofdifferent tooth numbers. At a given pitch and helix angle the spread orseparation of the grinding faces increases with increasing tooth numberof the workpiece.

Means for advancing the grinding wheels toward the surfaces engagedthereby at both ends of the grinding passes, as well as means forswinging the wheels very slightly on their pivot axes 106, 107 are notshown in this diagram. The diagram shown in Figs. 15 and 16 may be usedfor this purpose; or each grinding wheel may be advanced along its axisin place of the depthwise advance shown in the last-named embodiment.

In the embodiment of Figs. 15 and 16, the grinding wheels 90 and 91 arerotatably mounted in holders 120, 121, respectively, which are movablealong inclined ways 122, 123, respectively, of pivot members 124, 125.On each pivot member the ways extend in the direction of an element 127,127, respectively (Fig. 16), of the back cone 128, 129, respectively, ofthe grinding wheel. More broadly they extend along lines 126, 127intersecting the respective wheel axes at acute angles.

For dressing, a grinding wheel is advanced slightly along the ways 122,123 to advance the old grinding surface beyond its true position, andthe wheel is then dressed off. By using ways of the shown inclination,the advance of the wheel toward the dressing diamond does not have to besplit up into two motions, but is a single motion.

In accordance with this embodiment of my invention feed in the samedirection as for dressing is used for advancing a wheel toward thesurface engaged thereby adjacent both ends of each grinding path to easeoff the tooth ends.

Preferably the teeth are ground in unidirectional grinding passes orgrinding strokes, and the workpiece is rotated between successivegrinding strokes so that each wheel enters a different tooth space ineach successive stroke. This process requires disengaging the wheel completely from the workpiece at the end of each grinding stroke, andreengaging it before the start of the next grinding stroke. Thisdepthwise displacement of the grinding wheel, the clapping, is in adirection inclined at an acute angle to the axis of the grinding wheel,and in accordance with the invention it may be made in the samedirection in which the wheel is advanced for dressing. Also the advance.of the wheel for ease-off is made in the same direction as for clapping.

Each pivot member 124, is adjustable about a pivot axis 106, 107 and maybe oscillated thereon. In addition to the pivot itself, circular guideways 130, 131 are provided on a pair of slides 132, 133 to control thedisplacement of the pivot members 124, 125' thereon about the pivot axes106, 107, respectively.

The slides 132, 133 are adjustable on a common swivel plate 135 (Fig.16) toward and away from the work axis 35. The work may be mounted in achuck 136 (Fig. 15).

The swivel plate 135 rests on aslide 137 which is movable in thedirection of the axis 35 of the work piece and is adjustable thereonabout a central axis 138. The latter is parallel to the pivot axes 106,107 and intersects the axis 35 of the workpiece at right angles. Slide137 may be used for adjustment or for feed along the work axis 35. Slide137 and swivel plate 135 are not shown in Fig. 15.

The swivel plate 135 permits of displacing the two pivots 106, 107 sothat they have different positions lengthwise of the work axis 35, andthus provides a more universal machine than that illustrated in Fig. 14.

The clapping motion of each grinding wheel is effective by a barrel-typeearn 140 (Figs. 16 and 17) which is rigidly secured to a shaft 141 thatis rotatably mounted in each pivot member 120, 121. Shaft 41 extendsparallel to the inclined ways 122 or 123, and is geared to turn aroundonce per grinding cycle. Only one shaft 141 is shown in the drawings.The shaft 141 for pivot member 121 is identical with that shown, and isdriven in identical manner. Each shaft 141 performs as many completeturns as there are grinding strokes. It is driven from a fast-runningshaft 145 (Fig. 16) that extends parallel to the adjustment of the baseslide 137, through bevel gears 146, 147, 143, 149, 150, 151, 152, 153, aworm (not shown) Worm wheel 155, and connecting shafts. Bevel gears 152,153, the worm, and the worm wheel are mounted in the corresponding pivotmember 120 or 121.

Each barrel cam 140 acts on a conical roller that is mounted on a smallslide 161 (Fig. 17). This slide is adjustable in the holder 120 (or 121)lengthwise of the wheel element 126 or 127.

If desired the cam 140 may be shaped to do not merely the wheelclapping, but also to give the advance of the wheel adjacent both endsof the grinding passes for easeoff.

A more universal design is obtained by providing a specific ease-oficam. This cam 165 is secured to the barrel cam 140, and is adjustablethereon about its axis of roation. it contains coupling teeth 166engaging counterpart teeth provided on the cam 140. A nut 167 serves tohold the coupling teeth in engagement. The turning position of the cam165, that is, its timing, is changed by shifting the two sets of matingcoupling teeth after disengagement.

The cam 165 contains a slightly tapered working sur- 2,91o,sos

face which engages the flat abutment 170 (Fig. 17) secured to slide 161.During the grinding pass itself, the axial position of the slide 161 andof the grinding wheel is controlled by cam 165, while the barrel cam14%) controls the axial position during the remainder of the cycle. Thetrack on the barrel cam has to be kept wide enough in the portioncorresponding to grinding so that the cam 140 does not interfere withthe small motion constrained by the cam 165.

The working surface of the cam 165 is nearly fiat on account of itssmall taper, a taper possible because of the very small motion to beproduced by the cam. Contact between the cam and the plane abutment 170is intimate, and resembles contact in a bearing. High stresses arethereby avoided.

As the wheel moves toward the tooth surface engaged thereby during eachgrinding pass it should also be swung on its pivot 106 or 107 in timewith the grinding pass and in direct proportion with it. This is done bya disc earn 175 (Fig. 16) which is secured to the shaft 141 at one endthereof and which engages the roller 176. This roller is mounted on aslide 177 pressed toward the cam 175 by a spring 178. Slide 177 carriesanother roller 18!) which engages the straight slot 181 of a disc 182(Fig. The angularity of said slot can be adjusted by adjusting the disc182 angularly in an L-shaped part 183. The latter is adjustable aboutthe pivot axis 1% or 1617 on a circular flange 185 provided on the slide132, and can be clamped thereon.

When the disc 182 is adjusted so that its slot 181 is inclined to thedirection of travel of the roller 180 and the slide 177, the pivotmember carrying the slide 177 and the grinding wheel is rocked on itspivot axis during motion of the slide 177. It is rocked because slot 131and disc 182 are rigidly connected with the part 183 which is clamped tothe slide 132.

The amount of the minute swinging or rocking motion of each wheel iscontrolled with the adjustable inclination of the slot 181 of theassociated disc 182. The more the slot is inclined from the direction oftravel of the roller 180 the larger will be the rocking motion.

While the swing of the pivot members is adjustable for amount, theotherpart of the ease-off motion, namely, the part supplied by the cam 165 isadjustable only for timing. To enlarge or reduce its motion another camis substituted. A given cam produces essentially a given ease-ofi-at thetooth ends.

1 To facilitate cam changes, cam 165 is preferably open at one side likea horseshoe, and an opening may be provided in the pivot member 120.

While I have shown plain bearings in the diagrammatic views,anti-friction means may be used to ease the minute swinging motion onthe pivots 1%, 1117. Also springs may be used to keep out backlash.

In operation the feeding motion between the pair of rotating grindingwheels 90, 91 and the workpiece 21 is provided along and about the axisof the workpiece. At the end of each grinding stroke the wheels arewithdrawn in the direction of the elements 126, 127 of their respectiveback cones; and they are advanced again into working position in thatdirection just prior to the start of grinding contact. This clappingmotion is effected by the barrel cams which engage the conical rollers160. The rollers are adjustably but rigidly mounted on holders 124, 125,as the case may be.

Prior to dressing, the small slide 161 is adjusted downwardly in Figs.16 and 17 a small amount with respect to its holder, either by hand orautomatically. This adjustment lifts the holder upwardly so that itswheel is advanced along the cone element 126 or 127. It is then dressedoff and trued.

Ease-off at the tooth ends is attained by moving the wheel very slightlyalong element 126 or 127 at a varying rate at each grinding pass bycam165 to effect an advance over its position at zero ease-off adjacentboth 12 ends of the grinding pass. Simultaneously each grinding Wheel isswung on its pivot axis 106, 107 in time with the grinding stroke and inproportion to it. This is done by disc cam acting through roller 176 andslide 177.

The axis of the workpiece may be arranged either vertically orhorizontally; and the feed motion along the axis of the workpiece, thegrinding stroke or pass, may be performed by either the workpiece or thepair of grinding wheels. The turning motion about the axis of the workis preferably performed by the work.

Helical teeth can be ground by a process of continuous uniform rotationof the workpiece, or by any other known process and adding to it thesteps disclosed here.

While the invention has been described in connection with the grindingof gears which have parallel axes, and particularly helical gears withparallel axes, it applies to the grinding of side tooth surfaces ofother helical gears also, such as worms and other heelically-toothedmem: bers which mesh with their axes angularly disposed to the axes oftheir mating gears. 7

While the invention has been described, therefore, in connection withseveral different embodiments thereof, it will be understood that it iscapable of further modification, and this application is intended tocover any variations, uses, or adaptations of the invention following,in general, the principles of the invention and including suchdepartures from the present disclosure as come within known or customarypractice in the art to which the invention pertains and as may beapplied to the essential features hereinbefore set forth and as fallwithin the scope of the invention or the limits of the appended claims.

Having thus described my invention what I claim is:

1. In a machine for grinding the tooth surfaces of cylindrical gears, arotary work support, a base, a tool support adjustably pivoted on saidbase, a grinding wheel journaled on said tool support for rotation aboutan axis angularly disposed to the pivotal axis of said tool support,means for effecting relative movement between the tool and work supportsin the direction of the axis of rotation of the work support to effectalternate grinding and return strokes of the wheel, means for movingsaid wheel at a varying rate toward the tooth surface engaged therebyduring portions of each grinding stroke, and means for swinging the toolsupport about its pivot on each grinding stroke.

2. in a machine for grinding the tooth surfaces of cylindrical gears, arotary work support, a base, a tool support adjustably pivoted on saidbase, a grinding wheel journaled on said tool support for rotation aboutan axis angularly disposed to the pivotal axis of said tool support,said grinding wheel having an approximately plane grinding surface and aconical rear surface, means for adjusting said grinding wheel on saidtool support along an element of said rear surface, means for effectingrelative movement between the tool and Work supports to effect alternategrinding and return strokes of the wheel, means for moving said wheel ata varying rate toward the tooth surface engaged thereby along saidelement during portions of each grinding stroke, and means for swingingsaid tool support on its pivot in time with each grinding stroke.

3. In a machine for grinding the tooth surfaces of cylindrical gears, arotary work support, an adjustably pivoted tool support, a grindingwheel rotatabiy mounted on said tool support for rotation about an axisangularly disposed to the pivotal axis of said tool support, means fordisplacing said grinding wheel on said tool support along a straightline intersecting said axis of the grinding wheel at an acute angle,means for effecting reciprocating movements between the tool and worksupports in the direction of the axis of rotation of the work support toeffect alternate grinding and return strokes of the wheel, means formoving said wheel at a varying rate toward the tooth surface engagedthereby along said straight line} during portions of each grindingstroke, and means for swinging said tool support on its pivot in timewith each grinding stroke.

4. In a machine for grinding the tooth sides of cylindrical gears, arotary work support, a pair of pivoted tool supports, a holder mountedon each tool support, a pair of grinding wheels, that have approximatelyplane grinding surfaces, rotatably mounted on said holders with theirgrinding surfaces facing each other, said wheels being adapted to engagesimultaneously opposite tooth sides of the workpiece, means foreffecting a relative feed motion between said work support and saidgrinding wheels lengthwise of the tooth sides being ground, means fordisplacing each of said holders on its tool support in a directiontoward and away from the tooth side engaged by the grinding wheel thatis mounted on said holder during each grinding cycle, a pair of slideson which said tool holders are pivoted, each of said slides beingadjustable toward and from the axis of rotation of the work support, andthe pivot axes of said tool holders being parallel and each beingdisposed on the side of its wheel opposite to the grinding surface ofthe wheel.

5. in a machine for grinding the tooth sides of cylindrical gears, arotary Work support, a pair of pivoted tool supports, a holder mountedon each tool support, a pair of grinding wheels, that have approximatelyplane grinding surfaces, rotatably mounted on said holders with theirgrinding surfaces facing each other, said wheels being adapted to engagesimultaneously opposite tooth sides of the workpiece, means foreffecting a relative feed motion between said work support and saidgrinding wheels lengthwise of the tooth sides being ground, means fordisplacing each of said holders on its tool support in a directiontoward and away from the tooth side engaged by the grinding wheel thatis mounted on said holder during each grinding cycle, a pair of slideson which said tool holders are pivoted, each of said slides beingadjustable toward and from the axis of rotation of the work support, andthe pivot axes of said tool holders being parallel and having thegrinding wheels disposed between them, and the pivotal axis of each toolsupport being disposed at right angles to the axis of rotation of itsgrinding wheel.

6. In a machine for grinding the tooth sides of cylindrical gears, arotary work support, a pair of pivoted tool supports, a holder mountedon each tool support, a pair of grinding wheels, that have approximatelyplane grinding surfaces, rotatably mounted on said holders with theirgrinding surfaces facing each other, said grinding wheels being adaptedto engage simultaneously opposite tooth sides of the workpiece means fordisplacing each of said holders on its tool support in a directiontoward and away from the tooth side engaged by the respective grindingwheel, a pair of slides on which said tool holders are pivoted, each ofsaid slides being adjustable toward and from the axis of said worksupport, the pivotal axes of the two tool supports being parallel andhaving the grinding wheels disposed between them, and the pivotal axisof each tool support being disposed at an angle to the axis of rotationof its grinding wheel and being positioned on the side of its grindingwheel opposite to the grinding side of the wheel, means for effectingrelative reciprocatory movements between the tool and work supports inthe direction of the axis of the work support to effect alternategrinding and return strokes of the wheels, means for displacing saidholders at a varying rate during each grinding stroke, and means forswinging said tool supports simultaneously in opposite directions ontheir respective pivots during each grinding stroke and in timetherewith.

7. In a machine for grinding the tooth sides of cylindrical gears, arotary work spindle, a pair of pivoted tool supports, a holder mountedon each tool support, a pair of rotary grinding wheels, that haveapproximately plane working surfaces, mounted on the two holders withtheir axes of rotation approximately parallel and with theirapproximately flat working surfaces facing each other, said grindingwheels being adapted to engage simultane ously opposite tooth sides ofthe workpiece, guide mews for displacing each of said holders on itstool support in a direction toward and away from the tooth side engagedby its grinding wheel, a pair of slides laterally adjustable withrespect to the axis of rotation of the work spindle and on which saidtool supports are pivoted, the pivotal axes of the two tool supportsbeing parallel and having the grinding wheels disposed between them, thepivotal axis of each tool support intersecting the axis of rotation ofits grinding wheel at right angles and being disposed on the side of itsgrinding wheel opposite to the grinding surface of the wheel, means foreffecting relative reciprocatory movements between the work spindle andthe tool supports to effect alternate grinding and return strokes of thewheels, means for displacing each of said holders along said guide meansat a varying rate during each grinding stroke, and means for swingingsaid tool supports simultaneously in opposite directions on theirrespective pivot axes during each grinding stroke and in time therewith.

8. In a machine for grinding the tooth sides of cylindrical gears, arotary work spindle, a pair of pivoted tool supports, a holder mountedon each tool support, a pair of rotary grinding wheels, that haveapproximately plane grinding surfaces, rotatably mounted on said holderswith their grinding surfaces facing each other, said grinding wheelsbeing adapted to engage simultaneously opposite tooth sides of theworkpiece, guide means for displacing said holders on their respectivetool supports, each in a direction toward the tooth side engaged by thewheel supported on the holder, a pair of slides adjustable toward orfrom the axis of rotation of the work spindle and on which said toolsupports are pivoted on parallel axes, a common swivel plate supportingsaid slides, and a common slide on which said swivel plate rests and onwhichsaid swivel plate is angularly adjustable about an axis parallel tothe pivotal axes of said tool supports.

9. In a machine for grinding the tooth sides of cylindrical gears, arotary work spindle, a tool. support for rotatably mounting a grindingwheel, means for rotating said grinding wheel, means for effectingrectilinear feeding motion between said work spindle and tool support,means for turning said work spindle on its axis of rotation, arid meansfor swinging said tool support about a pivotal axis angularly disposedto the axes of rotation of the grinding wheel and work spindle in timewith and approximately in proportion to said feeding motion, saidpivotal axis having a position varying relatively to the bodily positionof the work spindle during said feeding motion.

10. The method of grinding a side tooth surface of a rotary cylindricalgear, which comprises providing a grinding wheel that has anapproximately plane working surface free of convex curvature, engagingsaid working surface with said tooth surface of the gear, rotating saidgrinding wheel on its axis, and effecting feeding motion between saidgrinding wheel and gear in the direction of the axis of rotation of thegear while simultaneously swinging the grinding wheel about a pivotalaxis angularly disposed to its axis of rotation in time with saidfeeding motion, to change the inclination of said plane working surfaceto said gear axis from one end of said tooth surface to the other end,said pivotal axis having a position varying relatively to the bodilyposition of the work during said feeding motion.

11. The method of grinding a side tooth surface of a rotary cylindricalgear which comprises engaging a grinding wheel, that has a grindingsurface of other than convex profile shape, with a side surface of thegear, rotating the wheel on its axis with said grinding surface inengagement with said side surface, and effecting rectilinear feedingmotion between the wheel and the gear, while relaf tively advancing thegrinding wheel toward said side surface adjacent both ends of saidfeeding motion, and while relatively swinging the wheel on an axisangularly disposed to the axes of the grinding wheel and of the gear, tochange the inclination of said grinding surface to the axis of saidgear.

12. The method of grinding a side tooth surface of a rotary helicallytoothed gear which comprises engaging a grinding wheel with said sidesurface, rotating the wheel on its axis with its working surface inengagement with said side surface, simultaneously rotating said gear onits axis of rotation, and simultaneously effecting feeding motionbetween the wheel and said gear in the direction of the axis of rotationof said gear in time with the rotation of said gear thereby to effect arelative helical motion about and in the direction of the axis of saidgear while relatively advancing the wheel toward said side surfaceadjacent both ends of said feeding motion, and while relatively swingingthe Wheel on an axis disposed at right angles to the axis of the wheeland fixed with respect to the wheel axis, said swinging motion beingcontinuous in one direction during said feeding motion.

13. The method of grinding a side tooth surface of a rotary helicallytoothed gear which comprises engaging a grinding wheel with said sidesurface, rotating the wheel on its axis with its working surface inengagement with said side surface, smultaneously rotating said gear onits axis of rotation, simultaneously effecting feeding motion betweenthe wheel and said gear in the direction of the axis of rotation of saidgear in time with the rotation of said gear, while relatively advancingthe wheel toward said side surface adjacent both ends of said feedingmotion, and while relatively swinging the wheel on an axis disposed atright angles to the axis of the wheel, the axis of swing of the wheelbeing disposed on the side of the wheel opposite to that which engagessaid side tooth SUI? face, and said swinging motion being proportionalto the axial distance travelled during said feed motion.

14. The method of grinding the side tooth surfaces of a rotary gear,which comprises engaging a grinding wheel, that has a grinding surfaceof other than convex profile shape, with said side tooth surface, androtating the wheel on its axis with said grinding surface in engagementwith side side tooth surface, while effecting a reciprocatory motionbetween the wheel and gear in the direction of the axis of rotation ofsaid gear to grind a side tooth surface of said gear on the relativestroke of the wheel in one direction axially of said gear and to returnthe wheel relatively to initial position on the return stroke,disengaging and reengaging the wheel and gear in a depthwise directionat the end and at the start, respectively, of each grinding stroke,rotating the gear on its axis between successive grinding strokes sothat the wheel enters a different tooth space of the gear on eachsuccessive grinding stroke, advancing the wheel toward the side toothsurface engaged thereby in said depthwise direction at a varying rateduring each grinding stroke, and swinging the wheel on an axis angularlydisposed to the axes of the wheel and of the gear in time with thegrinding strokes to produce crowned teeth.

15. The method of grinding a rotary helically toothed gear; whichcomprises engaging a grinding wheel that has a grinding surface that hasa slightly concave axial profile, with a side tooth surface of saidgear, and rotating the wheel on its axis with said grinding surface inengagement with said side tooth surface, while effecting a feed ingmotion between the wheel and said gear in the direction of and about theaxis of rotation of said gear in a relative helical path, relativelyadvancing the wheel toward the side tooth surface engaged thereby at avarying rate during said feeding motion, and swinging the wheel on anaxis angularly disposed to the axes of the wheel and of said gear, saidswinging motion being continuous in one direction during said feedingmotion.

16. The method of grinding a rotary helically toothed gear, whichcomprises engaging the working surface of a grinding wheel with a sidetooth surface of said gear, and rotating the wheel on its axis, whileeffecting a feeding motion between the wheel and said gear about and inthe direction of the axis of rotation of said gear in a relative helicalpath, relatively advancing the wheel toward said side tooth surface at avarying rate during said feeding motion, and simultaneously swinging theWheel about an axis angularly disposed to the axis of the wheel in timewith said feeding motion and continuously in one direction during saidfeeding motion.

17. The method of grinding a rotary helically toothed gear, whichcomprises engaging a grinding wheel, which has a slightly internalgrinding surface, with a side tooth surface of the gear, with saidgrinding surface in engagement with said side tooth surface, androtating the wheel on its axis, while effecting a feeding motion betweenthe wheel and the gear about and in the direction of the axis ofrotation of said gear in a relative helical path, relatively advancingthe wheel toward said side tooth surface at a varying rate during saidfeeding motion, and simultaneously swinging the wheel on an axisangularly disposed to the axes of the wheel and gear, said swingingmotion being continuous in one direction during said feeding motion.

18. The method of grinding a rotary gear, which comprises engaging agrinding wheel that has a working surface of other than convex profileshape, with a side tooth surface of said gear with said working surfacein engagement with said side tooth surface, and rotating the wheel onits axis, while effecting a feeding motion between the wheel and gear inthe direction of the axis of rotation of said gear, relatively advancingthe wheel toward said side tooth surface at a varying rate during saidfeeding motion, and simultaneously effecting a separate relativeswinging movement of the wheel relative to the gear on an axis angularlydisposed to the axes of the grinding wheel and of said gear, saidswinging motion being continuously in one direction during said feedingmotion.

19. The method of grinding a rotary gear, which comprises engaging agrinding wheel, that has a working surface of other than convex profileshape, with a side tooth surface of the gear with said working surfacein engagement with said side tooth surface, and rotating the wheel onits axis, while effecting a feeding motion between the wheel and gear inthe direction of the axis of rotation of said gear, relatively advancingthe wheel toward said side tooth surface adjacent both ends of thefeeding motion, said advance being along a straight line inclined at anacute angle to the grinding surface, and simultaneously effecting aseparate swinging movement of the wheel relative to the gear in timewith said feeding motion on an axis angularly disposed to the axes ofthe grinding wheel and of the gear.

20. The method of grinding a rotary gear which comprises engaging agrinding wheel, that has a working surface of other than convex profileshape, with a side tooth surface of the gear with said working surfacein engagement with said side tooth surface and rotating the Wheel on itsaxis, while effecting a relative reciprocatory motion between the wheeland said gear in the direction of the axis of rotation of said gear toproduce alternate grinding and return strokes, moving the wheel relativeto the gear depthwise in opposite directions at opposite ends of eachgrinding stroke along a straight line which intersects the axis of thewheel and which is inclined at an acute angle to its active grindingsurface, to disengage and engage, respectively, the wheel and gear atopposite ends of each grinding stroke, advancing the grinding Wheelalong said straight line at a varying rate during each grinding stroke,and simultaneously relatively swinging the wheel on an axis angularlydisposed to the axes of the wheel and gear in time with each grindingstroke.

21. The method of grinding a rotary helically toothed 3'3"?! Whichcomprises engaging the grinding surfaces of a pair of grinding wheels,each of which has a grinding surface of other than convex profile shape,with different tooth surfaces of the gear with their grinding surfacesfacing each other and with their axes of rotation paralleled and offsetand with the wheels displaced bodily relative to each other along theaxis of rotation of said gear, and effecting feeding motion between thewheels and said gear in a relative helical path about and in thedirection of the gear axis.

22. The method of grinding a rotary helically toothed gear whichcomprises engaging the grinding surfaces of a pair of grinding wheels,each of which has a grinding surface of other than convex profile shape,with different tooth surfaces of said gear with their grinding surfacesfacing each other and with their axes paralleled and inclined to theaxis of rotation of said gear and with the wheels displaced bodilyrelative to each other along the gear axis, each wheel being displacedfrom the average position of the two wheels in a direction toward theside of increased separation of the extended grinding surface from theaxis of said gear, and rotating the wheels on their respective axeswhile effecting feeding motion between said wheels and said gear in arelative helical path about and in the direction of the axis of saidgear.

23. The method of grinding a rotary helically toothed gear, whichcomprises engaging the grinding surfaces of a pair of grinding wheels,that have grinding surfaces of other than convex profile shape, withdifferent tooth surfaces of said gear with the axis of rotation of saidgear inclined to the axes of the wheels, rotating the wheels on theiraxes, and effecting feeding motion between the wheels and said gear in arelative helical path in the direction of and about the axis of rotationof said gear, advancing the wheels toward the surfaces engaged therebyat a varying rate during said feeding motion and simultaneously swingingthe wheels in opposite directions about axes angularly disposed to therespective wheel axes and to the axis of rotation of said gear in timewith said feeding motion.

24. The method of grinding a rotary helically toothed gear, whichcomprises engaging the grinding surfaces of a pair of grinding wheels,that have grinding surfaces of other than convex profile shape, withdifferent tooth surfaces of said gear, rotating the wheels on theirrespective axes, and effecting feeding motion in a relative helical pathbetween the wheels and gear in the direction of and angularly about theaxis of rotation, advancing the wheels respectively toward the surfacesengaged thereby at a varying rate during said feeding motion andsimultaneously swinging the wheels in opposite directions about parallelaxes angularly disposed to the axes of the wheels in time with saidfeeding motion.

25. The method of grinding a rotary cylindrical gear which comprisesengaging the grinding surfaces of a pair of grinding wheels, that havegrinding surfaces of other than convex profile shape, with differenttooth surfaces of said gear, rotating the wheels on their respectiveaxes, and effecting feeding motion between the wheels and gear in thedirection of the axis of rotation of said gear, advancing the wheelsindividually toward the respective tooth surfaces engaged thereby at avarying rate during said feeding motion, and simultaneously swinging thewheels in opposite directions about axes angularly disposed to theirrespective axes in time with said feeding motion to produce crownedteeth.

26. The method of grinding a rotary helically toothed gear whichcomprises engaging the grinding surfaces of a pair of grinding wheels,that have grinding surfaces of other than convex profile shape, withdifferent tooth surfaces of said gear with the axes of the wheelsapproximately parallel and with the grinding surfaces of the wheelsfacing each other and with the wheels displaced bodily relative to eachother along the axis of rotation of said gear, rotating the wheels ontheir respective axes, and effecting feeding motion in a relativehelical path between the wheels and said gear about and in the directionof the axis of rotation of said gear, advancing the wheels toward therespective tooth surfaces engaged thereby at a varying rate during saidfeeding motion, and simultaneously swinging the wheels in oppositedirections on separate axes in time with said feeding motion, the twolast-named motions of each grinding wheel being separate andindividually controllable.

27. In a machine for grinding the tooth surfaces of cylindrical gears, arotary work support, a pivoted tool support, a rotary grinding wheeljournaled on said tool support, said tool support having its pivotalaxis angularly disposed to the axis of rotation of the wheel, a slide onwhich said tool support is adjustably pivoted, said slide beingadjustable toward and from said work support, means for adjusting saidtool support and said slide in a plane perpendicular to the axis ofrotation of said work support, means for effecting a relativereciprocatory movement between the tool and work supports in thedirection of said axis of the work support to effect alternate grindingand return strokes of the wheel, means for approaching the grindingwheel to the tooth surface engaged thereby at a varying rate during eachgrinding stroke, and means for swinging said tool support about itspivot in time with each grinding stroke.

28. In a machine for grinding the tooth surfaces of cylindrical gears, arotary work support, a pivoted tool support, a rotary grinding wheeljournaled on said tool support, said tool support having its pivotalaxis angularly disposed to the axis of rotation of the wheel, a slide onwhich said tool support is adjustably pivoted, said slide beingadjustable toward and from said work support, means for adjusting saidtool support and said slide laterally toward and away from the axis ofrotation of said work support, means for effecting a. relativereciprocatory movement between the tool and work supports in thedirection of the axis of rotation of said work support to effectalternate grinding and return strokes of the wheel, a rotary shaft,means for rotating said shaft at a rate of one full turn for eachgrinding and return stroke of the wheel, a cam secured to said. shaftfor moving the tool support at a varying rate toward the gear toothsurface engaged thereby during portions of each grinding stroke, andother means operatively connected with said shaft for swinging said toolsupport on its pivot in time with each grinding stroke.

References Cited in the file of this patent UNITED STATES PATENTS1,474,500 Wingqvist Nov. 20, 1923 1,545,111 Wilder July 7, 19251,659,227 Wildhaber Feb. 14, 1928 1,669,919 Trbojevich May 15, 19282,025,688 Lees Dec. 24, 1935 2,048,520 Schurr July 21, 1936 2,319,117Drummond May 11, 1943 2,325,836 Drummond Aug. 3, 1943 2,347,998 DrummondMay 2, 1944 2,392,819 Gruenberg et a1. Jan. 15, 1946 2,597,648 Lucas May20, 1952

